1. Field of the Invention
The present invention relates to a method for detecting a defective disk of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces.
Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks. The disks are rotated by a spindle motor of the disk drive.
The bottom surface of each head has an air bearing surface that cooperates with an airflow generated by the rotating disks to create an air bearing between the head and the disk surface. The air bearing prevents or minimizes contact and resultant mechanical wear between the head and the disk. The field strength of the magnetic field detected by a head is inversely proportional to the height of the air bearing. It is therefore desirable to maintain a small air bearing while minimizing mechanical wear. The height of the air bearing is commonly referred to as the flying height of the head.
Each disk is typically constructed from a substrate that is coated with various layers of magnetic material. Manufacturing processes may introduce imperfections in the disk such as a disk curvature or surface waviness. Disk curvature or surface waviness may change the flying height of the head and increase the bit error rate (BER) of the drive. A drive with an unacceptable BER must be repaired or discarded. It would be desirable to detect and screen such disk imperfections before assembling the disk into a hard disk drive, to reduce the repair or discard rate of the drives.